The present invention relates generally to flow control for concentrating various video and other data into a single data stream. More particularly, the invention relates to filling the bandwidth of a digital data stream with pre-compressed data.
Generally, in digital communication systems, such as a satellite communication system, input information is transmitted from a broadcast center ("hub") to a remote site via a satellite, such as in Direct Broadcast Satellite ("DBS") transmission. Information input into the satellite communication system may include video (e.g. movies), interactive communications, promotional material (e.g. commercials), sporting events (including recorded replays), audio services, or other digitized data. The input information can be categorized into pre-recorded and live information. Live information could include signals from various feeds or sources, including sporting events, newscasts, or any inputs intended for immediate broadcast. Pre-recorded information could include movies, audio recordings, or time-shifted programming.
A typical DBS system employs one or more satellites to distribute the processed information. Each satellite may in turn provide one or more (typically a few) transponders available to support the DBS system. Each transponder operates within an assigned frequency range and optionally with an assigned phase. A broader frequency range is typically assigned to a particular satellite, which is in turn divided among the individual transponders to assure noninterfering operation. Uplink and downlink signals are typically assigned to different frequencies.
The data-carrying capacity of any radio frequency (RF) system is limited in part by the amount and character of RF spectrum that is available for use by the system. In general, for a given center frequency, the broader the assigned range or band of frequencies, the greater the potential information carrying capacity will be. In a DBS system, the spectrum allocated to the satellite as a whole may be viewed as a limitation on the information capacity of the satellite. Similarly, the portions of that spectrum allocated to individual transponders may be viewed as limitations respectively on each of the transponders. Thus, the space-based relay system may be viewed as a single high capacity conduit (satellite or satellite constellation), or it may be viewed as a number of individual conduits (e.g. transponder "channels"). For the purposes of the following discussions, either view may be adopted, although discussion of best mode embodiments will generally be in the context of a representative single transponder channel.
With reference to each individual conduit (e.g. transponder channel), the broadcast center transmits the input information to the satellite in a single output stream or signal comprising multiple data packets or frames of information. The output signal has a fixed bandwidth. Typically, to increase the amount of information that can be transmitted, the various input information signals will be compressed prior to transmission. Generally, pre-recorded information is allocated to one portion of the bandwidth of an output signal. The remaining bandwidth is allocated to live information or other information.
One method of concentrating compressed input information is known as Fixed Rate Flow Control ("FRFC"). In FRFC, a fixed amount of the bandwidth of the output signal is allocated to certain input information, such as pre-recorded information. The remaining bandwidth is then used for other input information, such as live broadcasts. However, the pre-recorded information may not use all of the allocated bandwidth of the output signal. Therefore, some portion of the allocated bandwidth may not be used.
Another method of concentrating compressed input information is known as Group Of Pictures ("GOP") Based Linear Control. In GOP, the amount of bandwidth allocated to pre-recorded information is determined by a linear function. For example, every sixth frame of a compressed information signal is examined to determine the bandwidth requirement, or data rate of the frame. A per frame slope is then calculated to determine the amount of bandwidth to allocate for each frame. However, GOP Based Linear Control may not be accurate in predicting the amount of bandwidth that will be used by the pre-recorded information. Thus, the pre-recorded information may be cropped (some information is not included) to fit within the allocated bandwidth. Cropping usually results in poor data quality. A certain amount of extra bandwidth may be allocated to each frame to avoid cropping, but this can result in unused bandwidth.
Therefore, there is a need for a system and method for allocating concentrated output bandwidth requirements in a predictive manner so that all bandwidth is efficiently used without cropping information.